Table ignores Container updates while painting (#12258)

Vaadin threw an IllegalStateException if a Container was updated while
Table was being painted. SQLContainer was known to invalidate its cached
size during a Table repaint, resulting in an ItemSetChangeEvent. This fix
has been copied over from how ComboBox handles this situation.

Change-Id: I04af71a5ea3844da245cb9e31ada4a30ff704619